Kind of new to third gen, even newer at rear differentials. I'm assuming it's a standard 9 bolt, but it has a dana fill plug in it. I tried finding pics of the Dana 44 rear end that came in some third gens, but couldn't find any. Just wondering if this is one. Need to know before I start ordering parts for it

 

That's just a 9 bolt with a Dana plug. A Dana 44 has 10 bolts in the cover.

 

Thanks so much!

 

And the dana also uses a metal pipe plug instead of the rubber.

 

85-88, but do you know which year, car and gear?

85-86 was in Trans Ams and likely has a 3.70 gear.

87-88 was in Formulas, Trans Ams, GTAs and IROCs, and is likely to have a 3.27 or 3.45.

 

Small detail, 89 was last yr for the 9bolt

 

True, but 89 had PBR brakes. The axle in this thread has the old iron brakes. It might be possible, maybe even probably that some 89 9-bolt disc axles received iron brakes, but 9-bolt disc axles were most likely only in the performance models, which would've probably received PBR brakes. I couldn't say for certain, because I haven't seen every 1989 9-bolt disc axle ever installed, so I don't speak in absolutes, but most likely lol.

 

I'm not sure what year it is. It came out of some car that was "supposedly" a 1LE but it's clearly not a 1LE rear. Also not sure how to figure out what year it is. Do you know how?

 

Hey thanks for that info! I wasn't sure what brake calipers and rotors to order. So I'm assuming the standard AC Delco non-performance rotors are the correct ones?

 

Correct on all counts: not a 1LE; has the standard 83-88 brakes, with 10.5" rotors and Delco (non-performance) iron metric e-brake calipers.

However, you could do the rear brake upgrade to the performance PBR brakes, if that's important to you. Flynbye.com has kits, probably Hawk's too.

To confirm the gear ratio you'd have to open the cover and read the numbers on the gears. Also, I'm thinking the bottom of the housing might have the RPO code cast into it, so you might look around where it says BORG WARNER on the underside.

If it's 3.70, which is possible, I've found some in the past and pulled one but ended up giving it away when I moved, but very unlikely these days, then it's from an 85-86 Trans Am.

Otherwise, 3.27 and 3.45 were available in 87-89. There was also a 2.77, but not likely in this case. 10-bolts had a low 3 something... ?3.08?, but I'm not sure if 9-bolts had one similar to that. I guess you'll know, if the gear isn't one of the three good ones, which it hopefully will be.

 

Here are the numbers stamped onto the housing by the Borg Warner, and then I think these are the numbers on the gears? I couldn't find anything else. I'm not super concerned with the gear ratio being high. It's just for a daily driver/cruiser. I don't race it or autocross, just wanted rear factory discs. Random question also that you might know about. The gasket for the cover as you can see is just some rubberized thing like they squeezed it out of a tube. Is that the correct type of gasket? I've seen rebuild kits and they have an actual gasket

 

The number cast into the housing is just that: the casting number of the housing casting. Doesn't tell you a thing about what's inside.

I'm not seeing any numbers anywhere on the gears that I can read, that might tell what they are. Usually they'll be stamped around the edge between the teeth and the flange on the carrier.

The usual 9-bolt ratios are 2.77 (BY FAR the most common... most of the 305 & 350 auto cars), 3.08 (some 305 5-spd), 3.27 (many 305 5-spd and some 350 auto, prob the next most common after 2.77), 3.45 (305 5-speed G92), and 3.70 (L69 5-speed, for all practical purposes 85 Firebird only except for a VERY FEW 86 Firebird, altogether VERY rare and by far the least common). Easy enough to figure out what you have: just count the teeth on the pinion and on the ring, and divide them by each other. If yours has for example 13 & 36, it's 2.77 (36 ÷ 13 = 2.7692307692307692307...); 11& 38, it's 3.45; etc. The stamping on the gear might look something like 36:11 which would be 3.27.

You'll HATE those 82-88 Delco-Moraine discs. They almost never work, not even as well as drums. The aluminum (89-up) PBRs are VASTLY better but require backing plates specific to the 9-bolt, and since those discs are 89 up but the last year of the 9-bolt was 89, there aren't many sets running around out there. If Ed is making repops of them, that might be an avenue to explore. Then all you have to do is come up with the calipers & rotors. 93-97 calipers might also work on the 89 backing plates, not sure one way or the other; they're very similar but I don't know if they bolt up. Alternatively check with Ed or bigbrakeupgrade.com for complete packages.

The 9-bolt has a posi system that wears out and ceases to function. Repairable but not a trivial matter.

Rebuild kits usually come with a gasket but RTV by itself works fine if done right.

 

Dude, super coincidence that you replied talking about that rear end. I went and picked up a rear hatch, tail lights, ground effects, rear bumper, and rear diff today. Paid $200 for it all and I'm pretty sure this rear diff is what you were talking about. It's from an 89 Iroc-Z. The discs are bigger than the discs on my other one and the calipers look different as well.

 

Yup that's a 89 9-bolt, w PBR brakes. Nice score.

What gears are in it? Posi still any good?

 

This one is 2.77 as well. At least I'm assuming. It has two tags, one about the posi fluid and one that says 2.77 along with some other gobbledygook on the other side of the diff cover. But I'm not concerned about gear ratios all that much. I just wanted rear discs. Apparently I found the good ones lol. I haven't checked Posi yet. It's still in my truck. I'll pull it out tonight and check once I get brake calipers off it. I know the other one spins both wheels in the same direction but I'm not sure how indicative that is of how well the Posi works. Maybe more of just a reassurance that it is, in fact, posi.

 

Nearly all (yes I'd say "all", but I've seen photos of one that wasn't) of the 9-bolts for these cars came with posi. Problem is, it uses metallic cones as the friction element, really a frustum of a cone, which wear around the circumference as they do their job; but eventually the "end" surface of the cone bottoms out inside the carrier, and the circumference no longer has friction against the carrier housing.

So, it can "have" posi, but still not act like it.

The solution is to cut down the end and add shims behind it to restore the spring tension and friction. Alternatively, there are new cones available for GTO rears, which are the same basic model but have minor differences; those can be machined to replace our originals without having to deal with re-shimming.

 

Do you have any resources as to what I should be looking at when I tear into the housing? I do want to check the Posi unit to make sure it's functioning. I assume if it fails it could send metal shavings, etc, into the gears which is obviously not good. I'm just almost next to clueless when it comes to a rear differential. I'm slowly learning all the different parts of the car. Sorry if I sound stupid lol

 

you can check the posi without doing a tear down. Spin the yoke and see what the discs do. If the discs spin the same direction the posi is functioning. If they spin opposite directions then the posi is not working.

we learn by asking questions, everyone on this board has been there!

 

Awesome, thanks! Yea the posi spins the right way. I wasn't sure if just spinning it by hand would be the same test as when it's under actual power. I think I will flush the fluid and I bought a TA cover for it. Apparently it secures the bearing "Caps"? and it adds some more fluid volume which I believe should keep it a little bit cooler.

 

cool. Yeah I have a cover like that on mine. Not sure if it works or if it’s just snake oil but it hasn’t grenaded yet 🤷‍♂️

 

Yea, it also looks cooler too, I guess lol. I'm just like a daily driver, weekend cruiser, so I don't anticipate it going out, but I figured I might as well do a flush and all that stuff before I install it

 

Nice score, that's the 2nd design of the 89 9bolt pbr caliper brackets. 1st design is a 2 piece with the dust shield

 

I'm learning new things every time I get replies. Is the second design or the first design better?

 

I ended up making a video to hopefully help some other people. Wanted to thank you guys again for all your help and understanding not everybody is an expert on these things lol

 

There was a tsb about the 1st design that brought on the stronger and stiffer 2nd design